The present invention relates generally to the art of electroforming, and more particularly to the art of electroforming a heating grid.
Electroforming of precision patterns, such as those used in optical systems, has been accomplished by several methods. For example, precision mesh patterns have been produced by electroplating onto a master pattern of lines formed by etching or ruling lines into a glass substrate and depositing a conductive material into the etched or ruled lines to form a conductive master pattern for electroplating. A major disadvantage of this method is the limitation on the fineness and precision of etching glass.
Photolithographic techniques have also been used to produce patterned electroforming mandrels. For example, a conductive substrate, such as a polished stainless steel plate, is coated with a layer of photoresist. A patterned photomask is placed over the photoresist, which is then exposed to actinic radiation through the mask, thereby creating a pattern of exposed and unexposed photoresist which is further developed. Either the exposed or the unexposed portions of the photoresist are removed, depending on whether a positive or negative pattern is desired, resulting in a conductive pattern on the substrate. An electroplating process is then carried out to form a replica of the conductive pattern which can thereafter be removed from the substrate. This method is also restricted in the uniformity and precision of lines which can be formed, as well as requiring reprocessing of the master pattern after limited usage.
U.S. Pat. No. 3,703,450 to Bakewell discloses a method of fabricating precision conductive mesh patterns on a repetitively reusable master plate comprising a conductive pattern formed on a nonconductive substrate and a non-conductive pattern formed in the interstices of the conductive pattern. A reproduction of the master pattern is formed by plating of a conductive pattern onto the master pattern within a matrix defined by the non-conductive pattern. The conductive metal master pattern is typically deposited onto a glass plate by evaporation of a metal such as chromium through a ruled pattern formed on a stencil material. The nonconductive pattern is formed by depositing a layer of photoresist over the conductive pattern coated side of the glass plate. By exposing the photoresist to actinic radiation through the conductive pattern coated substrate, exact registration of the conductive and nonconductive patterns is achieved. The photoresist layer is developed and the exposed portions are removed, leaving a pattern of photoresist over the conductive pattern. A silicon monoxide layer is then deposited over the entire surface of the glass plate, covering both the photoresist/conductive pattern coated portions and the exposed glass portions. Finally, the photoresist overlying the conductive pattern and the silicon monoxide overlying the residual photoresist material are removed, leaving the glass plate coated with a conductive metal pattern and an array of silicon monoxide deposits in the interstitial spaces in the conductive pattern. Replicas of the conductive pattern are then formed by electroplating.